Sensitive diazotype sheet for screen reflectography comprising a screen skin



y 1952 P. F. VAN DER GRINTEN 2,602,740

SENSITIVE DIAZOTYPE SHEET FOR SCREEN REFLECTOGRAPHY COMPRISING A SCREEN SKIN 7 Filed Dec. 29, 1948 5 ipierspezsed [mas vow? [fliers versed opaque areas (y scream 20122272- (screen 5km) 2612a 0/ adherence- INVENTOR LODEZWJK 'PETER FRANS VAN DER Gram-ram BY PM W ATTORNEYS Patented July 8, 1952 UNITED STATES PATENT DFFICE SENSITIVE DIAZOTYPE SHEET FOR SCREEN REFLECTOGRAPHY COM-'- PBISING A SCREEN SKIN pany of the Netherlands Application December 29, 1948, Serial No. 67,994 In the Netherlands December 31, 1947 12 Claims.

The invention relates to a sensitized diazotype sheet for screen reflectography, the said sheet comprising a screen which, besides portions substantially pervious to light to which the diazo compound is sensitive, has only portions substantially impervious to the said light, the latter portions being connected. to a skin in such a manher that upon removal of the skin substantially all the last-mentioned portions are also removed. Such a sheetis referred to hereinafter as a screen skin sheet, such a skin as a screen skin. Screen skin sheets of this type have been described in copending U. S. applications Serial Nos. 705,309 and 705,310, filed October 24, 1946.

For screen r-eflectography, as has already been stated, the screen should consist exclusively of portions substantially impervious to light to which the sensitized layer is sensitive and portions substantially pervious to such light, without transitions. Because the light used in practice is always more or less diffused, the contact between screen and sensitized layer should satisfy high demands. These demands of close contact are of a special nature in the case of diazotype sheets, in view of the development of nitrogen during exposure, which may tend to diminish the contact necessary up to the end of the exposure, especially in the case of screen skin sheets. In addition, the removal of the screen skin (the descreening) after exposure is in practice a factor of importance; after the exposure the skin (with screen) has to be separated from the remaining part of the sheet. Up to thepresent this was effected by stripping the skin off dry, for which a thick and consequently expensive skin (of at least g./m. is required, or by making use of adhesive surfaces, which entails additional expense.

The principal object of this invention is to provide screen skin sheets of the type mentioned which retain their unitary structure under normal handling and during exposure, but from I which the screen skin can be removedafter exposure in a much simpler manner than by-pull ing the screen to strip it from the remainder of the sheet. Another object is to provide such screen skin sheets which satisfy the practical requirements of diazotype screen r'efiectography and yet can make efficient use of very thin and relatively inexpensive screensk-ins.

It has been found that sensitized diazotype sheet materialsfulfillingi these'needs can be obtained by joining a skinunited with a light screen with a flexible base or film carrying a light-sensitive diazo layer. over one side, under a certain degree of. cohesion which can be so determined that the sheet components firmly cohere as a unit" under normal conditions of handling and exposure but" separate readily when the sheet is subjected to a suitabl'e' sharp Bending spewtion. The necessary cohesioncan' be measured and expressed quantitatively in terms of the. creasing ability of the screen skin sheet, by' use of a 'Schiefer flexometer as described in Research Paper No. 555 of the United States Bureau of Standards. It has been found that. the re;- quired combination of properties canv be (Sbtained by making screen skin sheets with. a creasing ability in the range of 3 to 15,

-measured as the angle between the legs of the flexometer with the top (apex) of the bend of the sheet at a distance of 2.5 cm.- from the joint of the flexometer and with the sheet bent between said legswith its screen skin side inward. When the creasing ability is smaller than about 23 it is impractical to remove the screen by a bending operation, and when it exceeds about 15 the screen adheres tooloosely to fulfill the requirements of handling and exposure.

The screen skin sheets embodying this invention have been found to be particularly satisfactory when the said creasing ability is at least 6 and at most 10.- A screen skin with a weight between 2 and 8 g./ni. and preferably between 4 and 6 g'l/m. is the most suitable. When applying the present invention no thick screen'skin is, therefore, required. The advantage of the dia'z'otype screen skin sheet made according to this invention resides chiefly in the fact that, while for practical purposes, especially for manipulation and exposure of the screen skin sheet, the screen skin adheres sufiicien'tly solidly, the screen skin sheetrnay' be (lo-screened in a very simple manner hitherto unknown, viz. by a mechanical folding, bending, wrinkling, flexing or creasing operation, e. g. by passing the screen skin sheet along its screen skin side over a sharp edge. By creasing is meant a visible diminution of the close contact between the screen skin and the remainder of the sheet, which demonstrates itself similarly to a visible break or crack in flexural orbe'nding tests with ordinary materials. The creasing ability oil a sheet-=tlie beginning of the creasing (breaking or cracking resulting in the diminution of contaco-in this sense occurs as soon as the revolving leg in the fiexometer forms with thefixed leg an angle which produces this characteristic in a given screen skin sheet. In order to obtain values for creasing ability permitting of com parison it is, of course, necessary to dispose the screenskin sheet always in the same manner between the legs of the flexometer. This manner has been so defined above that the top (apex) of the bend of the screen sk'in sheet-is to be at a distance of 2.5 cm. from the joint of the flexometer, while the screen skin is to be on the in.- side of the bend.

The invention relates both toscreenskin'sheets in which the area of contact betweenscreen skin 3 and remainderof the sheet is substantially fiat and to screen skin sheets in which the said area has the form of a relief corresponding with the screen structure. Both types of screen skin sheets have been described in the applications mentioned before. In view of the advantages it presents, the latter type is preferred.

In the accompanying drawing,

Fig. 1 is a diagram of one embodiment of an apparatus arrangement for use in producing a screened sensitized diazotype sheet accordingto the invention;

Fig. 2 is a diagram of a relief pattern provided on the surface of the cylinder of Fig. 1;

Fig. 3 is an enlarged diagrammatic cross-section through a screened sheet made according to one embodiment of the invention, the legends associated with this figure describing component parts of the sheet structure; and

Fig. .4 is a diagram of the principle of operation of a Schiefer fiexometer as used to determine the creasing ability of the new screened sheets. I

The screened sheet. illustrated in Fig. 3 'comprises a flexible transparent base film 20 formed over. one side with a relief impression and carrying over that side a light-sensitive diazolayer 2i and a covering screen skin which is, adhered firmly but separately to the sensitized side of the transparent base by means either of its area of contact therewith or of a suitable thin adhesive film as diagrammed at 22. The screen skin itself is composed of a transparent skin 23 united with interspersed opaque areas at 24 and itself presenting at 25 transparent areas interspersed with the opaque areas so as to constitute a screen pattern.

Example I On the surface I of a cylinder (Fig. 1) a relief as shown in Fig. 2 has-been provided, consisting of elevations 2 having a height of 15 mu, a horizontal section of 40 x 40 mu and a period of 80 mu.

The cylinder slowly rotates and carries along at 3 a filler of 20% of carbon black, 4% of asphalt and 1.75% of diethylene glycol in toluene,

This dries at once. At 4 the upper surfaces of the elevations 2 are cleaned. The carbon blackasphalt mixture left at the bottom has a weight of about 2 g./m. At 5 a thin varnish layer consisting of 4% of cellulose acetate-butyrate in ethyl acetate and I of diethylene glycol is 'applied,'whichis dried at 6 and 1, by heat radiation, to a screen skin weighing about 5 g./m. inclusive of the carbonblack and the asphalt. On this screen skin an adhesive layer is applied at 15, consisting of 0.3 of polyvinyl acetate resin (trade name: Gelva V 2 1/2) in toluene, which is dried and heated at IE.

Now a sensitized diazotype film is introduced at 8. This film consists of a film of cellulose acetate of 75 g./m. superficially saponified and subsequently sensitized with an aqueous solution of 5% of 1-diazo-3-chloro-4-dimethyl amino benzene chloride 1% of alum of ethyl alcohol.

At 8 the film passes with its sensitized side turned to the cylinder.

At 9 pressure is applied and after cooling the completed screen skin sheet leaves the cylinder at l0.

When the ability of creasing is measured in the Schiefer fiexometer (Fig. 4) while the screen skin sheet is bent towards its screen skin side with its curve at a distance I I (2.5 cm.) from the joint l2, it is observed that when the legs l3 and H! of the flexometer form together an angle of 15, a perceptible diminution of the close contact of the screen skin (creasing, breaking or cracking) sets in, a diminution which increases according as the angle becomes smaller and has become clearly visible when the angle is about 10. The screen skin sheet obtained consequently has an ability of creasing of 15-10". The weight of the screen skin is 5 g./m.

The screen skin sheet with its screen skin side towards the source of light and its other side in contact with the original to be copied is exposed, at a distance of 5 cm, to the light of a high-pressure mercury vapour lamp with a current consumption of about 20 watts per cm. of luminous length of the lamp. After the exposure, which takes about 1 minute, the screen skin sheet while being sharply bent on a sharp edge, is passed under tension over said edge. The screen skin loosens and can be removed by hand, taking along with it the covering screen portions. It would be practically impossible to remove the screen skin by mere stripping off.

Thereupcn development takes place by the application of a layer of 10 g./m. of an aqueous developer of the following composition:

0.8% of phloroglucinol 0.8% of resorcinol 3% of sodium carbonate 6% of sodium thiosulphate 2 of thiourea r 1 of potassium rhodam'de 0.2% of the sodium salt of isopropyl naphthalene sulphonic acid.

Example II A film of cellulose acetate of g./m. carrying on one side a relief as illustrated in Fig. 2 for the surface of cylinder 1, is superficially saponified on the relief surface and subsequently sensitized with an aqueous solution of z 6% of l-diaz0-3-methyl-4dimethyl amino benzene chloride 2% of oxalic acid 1 of phenol 20% of ethyl alcohol.

On the relief a mixture of toluene with 20% of carbon black 4% of Syrian asphalt and 1.75% of diethylene glycol is now applied; after drying, the tops of the relief are cleaned with smooth, soft leather. Now the screen side is covered with a thin layer of a varnish consisting of 4 parts by weight of cellulose acetate-butyrate parts by Weight of ethyl acetate 1 part by weight of ethylene glycol,

and dried again, so that on the sensitized diazotype film a screen skin is formed of about 4 g./m. including the carbon black asphalt constituents incorporated in the varnish film. The screen skin sheet thus obtained has an ability of creasing of about 7-8 in the Schiefer flexometer, defined as indicated above.

' After:exposureandde=screemngas=inExampie I development takes place in ammonia, vapour I the'examples giventhe creasing' abiiity produ'c'ed may, i f desired, be varied; it'may; for'example; be reduced by addition-of small amounts 1. A screened sensitized diazotype sheet for refiect'ography comprising a-flexible base transparent to the exposing light 7 carrying over one side a light-sensitive diazo layerand a firml'y'adhering-f but separable skin united with a screen the pattern of which consists of a myriadiof irrterspersed minute areas' respectively transparent and opaque to such light, said sheet possessing-a creasing ability, as hereinbefore defined; of' between 3 and so that the screen skin and the remainder of the sheet cohere as a unit during handling and exposure but separate when the sheet is drawn over a sharp edge while bent sharply thereover with the screen skin side inward.

2. A'screened sensitized diazotype sheet for refiectography comprising a flexible base transparent to the exposing light carrying over one side a light-sensitive diazo layer and a firmly adhering but separable skin united with a screen the pattern of which consists of a myriad'of interspersed minute areas respectively transparent and opaque to such light, said sheet possessing a creasing ability, as hereinbeiore defined, of between 6 and 10 so that the screen skin and the remainder of the sheet cohere as a unit during handling and exposure but separate when the sheet is drawn over a sharp edge while bent sharply thereover with the screen skin side inward. I

3. A screened sensitized diazotype sheet for refiectography comprising a flexible base transparent to the exposing light carrying over one side a light-sensitive diazo layer and a firmly adhering but separable skin united with a screen the pattern of which consists of a myriad of interspersed minute areas respectively transparent and opaque to such light, said sheet possessing a creasing ability, as hereinbefore defined, of between 3 and 15 so that the screen skin and the remainder of the sheet cohere as'a unit during handling and exposure but separate when the sheet is drawn over a sharp edge while bent sharply thereover with the screen side inward, the screen skin unit having a weight of about 2 to 8 grams per square meter.

4. A screened sensitized diazotype sheet for reflectography comprising a fiexible base transparent to the exposing'light carrying over one side a light-sensitive diazo layer and a firmly adhering but separable skin united with a screen the pattern of which consists of a myriad of interspersed minute areas respectively transparent and opaque to such light, said sheet possessing a creasing ability, as hereinbefore defined, of between 3 and 15 so that the screen skin and the remainder of the sheet cohere as a unit during handling and exposure but separate when the sheet is drawn over a sharp edge while bent sharply thereover with the screen skin side inward, the screen skin unit having a weight of about 4 to 6 grams per square meter.

5. A screened sensitized diazotype sheet for reflecto'g raphyi comprisinga fiexibla-basextransparent 'tOz'thG exposing light carrying over: One; side a light-sensitive diazo-layer and a iirmly'-"ad=-;v hering but separable skin unitedwith a screen the pattern of which consists of a myriad ofjinaterspersed minute. areas respectively transparent and opaque'to-sucli light; said sheetpossessinga; creasing" ability,- as hereinbefor-e defined; of be tween 3 and --l-5= so'that the screensk-in and=the remainder? of the sheet cohere. as a unit. during handling exposurebut separate when; the sheet is jdrawn overa sharp edgewhile bent sharply thereoverwith the screen skin side iii! ward,theareaof contact between th screen skin and the remainder of the sheet having-the form or a depth relief" corresponding with the screen pattern.

6; The method of de-screening a screened die. azot'ype -sheet as describedin claim 1, which comprises: drawing the sheet over a sharp edge while holding it sharply bent thereover with the screen skin side inward, and removing the screen skin thus loosened.

7. A screened sensitized diazotype material comprising a flexible cellulosic bas transparent to the exposing light, carrying over one side a light-sensitive diazo layer and a thin firmly ad hering cellulosic skin which is transparent to said light and united with a myriad of distinct minute deposits opaque thereto to constitute a light screen, the screen skin having a weight of only about 2 to 8 grams per square meter and being strongly held to the sensitized side of the base by a frangible connection which is severable by drawing the material over a sharp edge while holding it bent sharply thereover with the screen skin side inward, said sheet possessing a creasing ability, as hereinbefore defined, of between 3 and 15.

8. A screened sensitized diazotype material comprising a flexible cellulosic base transparent 'to the exposing light, carrying over one side a light-sensitive diazo layer and a thin firmly adhering cellulosic skin which is transparent to said light and united with a myriad of distinct minute deposits opaque thereto to constitute a light screen, the screen skin having a weight of only about 2 to 8 grams per square meter and being strongly held to the sensitized side of the base by a frangible connection which is severable by drawing the material over a sharp edge while holding it bent sharply thereover with the screen skin side inward, the flexible base and the skin, respectively, being composed principally of cellulose acetate and cellulose acetate-butyrate, said sheet possessing a creasing ability, as hereinbefore defined, of between 3 and 15.

9. A screened sensitized diazotype material comprising a flexible cellulosic base transparent to the exposing light, carrying over one side a light-sensitive diazo layer and a thin firmly adhering cellulosic skin which is transparent to said light and united with a myriad of distinct minute deposits opaque thereto to constitute a light screen, the screen skin having a weight of only about 2 to 8 grams per square meter and being strongly held to the sensitized side of the base by a frangible connection which is severable by drawing the material over a sharpedge while holding it bent sharply thereover with the screen skin side inward, said frangible connection com- 10. A screened sensitized,diazotypematerial as described in claim 9, the adhesive being a transparent polyvinyl ester composition.

11. A screened sensitized diazotype material comprising a flexible cellulosic base transparent to the exposing light, carrying over one sidea light-sensitive diazo layer and a thin firmly adhering cellulosic skin which is transparent to said light and united with a myriad of distinct minute deposits opaque thereto to constitute a light,

screen, the screen skin having a weight-of only about ,2 to 8 grams per square meter and being strongly held to the sensitized side of the base by a frangible connection which is severable by drawing the material over a sharp edge while holding it bent sharply thereover with the screen skin side inward, said frangible connection comprising a myriad of interfitting minute regularly found elevations and recesses on meeting surfaces respectively of the screen skin and the sensitized side of the base, said sheet possessing a "creasing ability, as hereinbefore defined, of between 3 and 15. t g j 12. A screened sensitized diazotyp material as described in claim 11, the elevations on thescreen skin being the screen-forming opaque deposits.

LODEWIJK PIETER FRANS VAN DER GRINTEN.

REFERENCES CITED The following references are of record in. the file of this patent:

UNITED STATES PATENTS 

1. A SCREENED SENSITIZED DIAZOTYPE SHEET FOR REFLECTOGRAPHY COMPRISING A FLEXIBLE BASE TRANSPARENT TO THE EXPOSING LIGHT CARRYING OVER THE SIDE A LIGH-SENSITIVE DIAZO LAYER AND FIRMLY ADHERING BUT SEPARABLE SKIN UNITED WITH A SCREEN THE PATTERN OF WHICH CONSISTS OF A MYRIAD OF INTERSPERSED MINUTE AREAS RESPECITIVELY TRANSPARENT AND OPAQUE TO SUCH LIGHT, SAID SHEET POSSESSING A CREASING ABILITY, AS HEREINBEFORE DEFINED, OF BETWEEN 3* AND 15* SO THAT THE SCREEN SKIN AND THE REMAINDER OF THE SHEET COHERE AS A UNIT DURING 